# Structs in Modules

**URL:** <https://discourse.julialang.org/t/structs-in-modules/34317>\
**Category:** New to Julia\
**Created:** [February 7, 2020, 6:13pm UTC](https://discourse.julialang.org/t/structs-in-modules/34317 "2020-02-07T18:13:08Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![squirrel](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@squirrel](https://discourse.julialang.org/u/squirrel)\
**Post date:** [February 7, 2020, 6:13pm UTC](https://discourse.julialang.org/t/structs-in-modules/34317/1 "2020-02-07T18:13:08Z")

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So I have two modules that I wrote, `SparseRowEchelon.jl` and `SparseBasis.jl`.  
`SparseRowEchelon` includes a `struct` that is also used in `SparseBasis`, and this causes a problem when my main file tries to call a function in `SparseBasis`.

`SparseRowEchelon.jl` looks like this:

```julia
module SparseRowEchelon

export foo, SparseRREF

using SparseArrays

struct SparseRREF
    T::Vector{SparseVector}
    isPiv::BitArray
end

# some functions, including foo()

end

```

and `SparseBasis.jl` looks like this

```julia
module SparseBasis

using SparseArrays
include("SparseRowEchelon.jl")
using .SparseRowEchelon

export get_spbasis

function get_spbasis(sparse_rref::SparseRREF)
    # blah blah blah
end

end

```

So `SparseBasis` is using a struct that I defined in `SparseRowEchelon`.

The problem is when I go to use these modules in another file, called `modeling.jl`.

```julia
include("SparseRowEchelon.jl")
using .SparseRowEchelon

my_sparce_rref = foo() # does a thing that returns type `SparseRREF`

include("SparseBasis.jl")
using .SparseBasis

get_spbasis(my_sparce_rref)

```

This returns the error that they cannot find method `get_spbasis`.

> MethodError: no method matching get\_spbasis(::SparseRREF)  
> Closest candidates are:  
> get\_spbasis(!Matched::Main.SparseBasis.SparseRowEchelon.SparseRREF) at [path to SparseBasis.jl]:10

That is the method I want it to use, but why doesn’t it want to use it? And how can I fix it?

Thanks!

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<div class="post-metadata">

**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [February 7, 2020, 7:14pm UTC](https://discourse.julialang.org/t/structs-in-modules/34317/2 "2020-02-07T19:14:15Z")

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You `include` the file `"SparseRowEchelon.jl"` twice; once inside `SparseBasis` and once in `Main` (i.e. the REPL). This means that you define the module and structs in there twice, so `SparseRowEchelon.SparseRREF` is NOT the same struct as `SparseBasis.SparseRowEchelon.SparseRREF` are different structs. `get_spbasis` is defined for `SparseBasis.SparseRowEchelon.SparseRREF` and not `SparseRowEchelon.SparseRREF` and hence you get a method error.

You should only include the same file one time, generally speaking. Then you have to decide if you want to do it inside your other module, or only at the outside as a separate module.

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<div class="post-metadata">

**Author:** ![squirrel](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@squirrel](https://discourse.julialang.org/u/squirrel)\
**Post date:** [February 7, 2020, 7:19pm UTC](https://discourse.julialang.org/t/structs-in-modules/34317/4 "2020-02-07T19:19:53Z")

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So if the `struct` is being used in both `SparseBasis` and `SparseRowEchelon` and also in my main file, what would you say is the best way of handling this?

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<div class="post-metadata">

**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [February 7, 2020, 7:30pm UTC](https://discourse.julialang.org/t/structs-in-modules/34317/5 "2020-02-07T19:30:17Z")

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You have to decide where you define it, and then use that same definition at all the places. I would just have everything in the same module, e.g.

```julia
module SparseBasis
...

include("SparseRowEchelon.jl")
using .SparseRowEchelon

end

```

and then when you use it in the REPL you just include that file.

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<div class="post-metadata">

**Author:** ![squirrel](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@squirrel](https://discourse.julialang.org/u/squirrel)\
**Post date:** [February 7, 2020, 7:53pm UTC](https://discourse.julialang.org/t/structs-in-modules/34317/6 "2020-02-07T19:53:13Z")

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That works. Thanks! 😄

(Also needed to add SparseRowEchelon’s exports to SparseBasis.)